Nonaqueous electrolyte battery, battery pack and rechargeable vacuum cleaner

ABSTRACT

A nonaqueous electrolyte battery includes a positive electrode, a negative electrode and a nonaqueous electrolyte. At least one of the positive electrode and the negative electrode comprises a current collector made of aluminum or an aluminum alloy and an active material layer laminated on the current collector. The active material layer contains first active material particles having an average particle diameter of 1 μm or less and a lithium diffusion coefficient of 1×10 −9  cm 2 /sec or less at 20° C., and second active material particles having an average particle diameter of 2 to 50 μm. A true density of the second active material particles is larger by 0.01 to 2.5 g/cm 3  than a true density of the first active material particles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. Ser. No. 11/756,259 filed May 31, 2007,and claims the benefit of priority under 35 U.S.C. §119 from JapanesePatent Applications No. 2006-155088 filed Jun. 2, 2006 and No.2007-050389 filed Feb. 28, 2007, the entire contents of each of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a nonaqueous electrolyte battery, a batterypack using the nonaqueous electrolyte battery and a rechargeable vacuumcleaner.

2. Description of the Related Art

Use of a negative electrode active material with an average particlediameter of 1 μm or less for a nonaqueous electrolyte battery has beeninvestigated. However, a negative electrode using the negative electrodeactive material is deficient in impregnating ability of the nonaqueouselectrolyte since the negative electrode active material is compactlypacked in the negative electrode, and may bring up a problem ofdeterioration of cycle performance.

JP-A 2004-119218 (KOKAI) and JP-A 2002-100354 (KOKAI) have reported thatcharacteristics of respective active materials can be maximally exertedby using a mixture of a plurality of active materials having differentaverage particle diameters from one another.

JP-A 2004-119218 (KOKAI) describes that discharge performance at a largeload current can be improved by controlling the press density of largediameter particles and small diameter particles of lithium-cobaltcomposite oxide in the range of 2.8 to 3.2 g/cm³ and 2.7 to 3.2 g/cm³,respectively. The press density described in JP-A 2004-119218 (KOKAI)refers to an apparent press density obtained when a powder of theparticles is compressed at a pressure of 0.3 t/cm², and differs from atrue density.

On the other hand, JP-A 2002-100354 (KOKAI) discloses controlling theproportion of the number of fine particles with a particle diameter ofless than 1 μm in the range of 7 to 85% by pulverizing agglomeratelithium titanate obtained by a solid-solid reaction in order to improvedischarge capacity and heavy drain discharge performance of thenonaqueous electrolyte secondary battery. In JP-A 2002-100354 (KOKAI),the true densities of the particles constituting the mixture are thesame since the mixture of the particles with a particle diameter of lessthan 1 μm and the particles with a particle diameter of 1 μm or more isobtained by pulverization.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda nonaqueous electrolyte battery comprising:

a positive electrode;

a negative electrode; and

a nonaqueous electrolyte,

wherein at least one of the positive electrode and the negativeelectrode comprises:

a current collector made of aluminum or an aluminum alloy; and

an active material layer which is laminated on the current collector,the active material layer containing

first active material particles having an average particle diameter of 1μm or less and a lithium diffusion coefficient of 1×10⁻⁹ cm²/sec or lessat 20° C. and

second active material particles having an average particle diameter of2 to 50 μm,

a true density of the second active material particles is larger by 0.01to 2.5 g/cm³ than a true density of the first active material particles.

According to a second aspect of the present invention, there is provideda nonaqueous electrolyte battery comprising:

a positive electrode;

a negative electrode comprising a current collector made of aluminum oran aluminum alloy and an active material layer laminated on the currentcollector, the active material layer containing

first active material particles that have an average particle diameterof 1 μm or less and are represented by Li_(4+x)Ti₅O₁₂ (0≦x≦3) and

second active material particles having an average particle diameter of2 to 50 μm, and a true density of the second active material particlesbeing larger by 0.01 to 2.5 g/cm³ than a true density of the firstactive material particles; and

a nonaqueous electrolyte.

According to a third aspect of the present invention, there is provideda nonaqueous electrolyte battery comprising:

a positive electrode comprising a current collector made of aluminum oran aluminum alloy and an active material layer laminated on the currentcollector, the active material layer containing

first active material particles that have an average particle diameterof 1 μm or less and are represented by Li_(y)Mn₂O₄ (0≦y≦1) and

second active material particles having an average particle diameter of2 to 50 μm, and a true density of the second active material particlesbeing larger by 0.01 to 2.5 g/cm³ than a true density of the firstactive material particles;

a negative electrode; and

a nonaqueous electrolyte.

According to a fourth aspect of the present invention, there is provideda battery pack comprising a nonaqueous electrolyte battery comprising apositive electrode, a negative electrode and a nonaqueous electrolyte,

wherein at least one of the positive electrode and the negativeelectrode comprises:

a current collector made of aluminum or an aluminum alloy; and

an active material layer which is laminated on the current collector,the active material layer containing

first active material particles having an average particle diameter of 1μm or less and a lithium diffusion coefficient of 1×10⁻⁹ cm²/sec or lessat 20° C., and

second active material particles having an average particle diameter of2 to 50 μm,

a true density of the second active material particles is larger by 0.01to 2.5 g/cm³ than a true density of the first active material particles.

According to a fifth aspect of the present invention, there is provideda battery pack comprising a nonaqueous electrolyte battery comprising apositive electrode, a negative electrode and a nonaqueous electrolyte,

wherein the negative electrode comprises a current collector made ofaluminum or an aluminum alloy and an active material layer laminated onthe current collector, the active material layer containing

first active material particles that have an average particle diameterof 1 μm or less and are represented by Li_(4+x)Ti₅O₁₂ (0≦x≦3) and

second active material particles having an average particle diameter of2 to 50 μm, and a true density of the second active material particlesis larger by 0.01 to 2.5 g/cm³ than a true density of the first activematerial particles.

According to a sixth aspect of the present invention, there is provideda battery pack comprising a nonaqueous electrolyte battery comprising apositive electrode, a negative electrode and a nonaqueous electrolyte,

wherein the positive electrode comprises a current collector made ofaluminum or an aluminum alloy and an active material layer laminated onthe current collector, the active material layer containing

first active material particles that have an average particle diameterof 1 μm or less and are represented by Li_(y)Mn₂O₄ (0≦y≦1) and

second active material particles having an average particle diameter of2 to 50 μm, and a true density of the second active material particlesis larger by 0.01 to 2.5 g/cm³ than a true density of the first activematerial particles.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a partially cut perspective view showing a nonaqueouselectrolyte battery according to a first embodiment;

FIG. 2 is a partially cut perspective view showing another nonaqueouselectrolyte battery according to the first embodiment;

FIG. 3 is a schematic illustration of a magnified cross section of amain part of an electrode group of the nonaqueous electrolyte batteryshown in FIG. 2;

FIG. 4 is a schematic perspective view of the stacking type electrodegroup used in the nonaqueous electrolyte battery according to the firstembodiment;

FIG. 5 is an exploded perspective view of the battery pack according toa second embodiment;

FIG. 6 is a block diagram showing an electric circuit of the batterypack shown in FIG. 5;

FIG. 7 is a schematic illustration of a series hybrid car according to athird embodiment;

FIG. 8 is a schematic illustration of a parallel hybrid car according tothe third embodiment;

FIG. 9 is a schematic illustration of a series-parallel hybrid caraccording to the third embodiment;

FIG. 10 is a schematic illustration of an automobile according to thethird embodiment;

FIG. 11 is a schematic illustration of a hybrid motorcycle according tothe third embodiment;

FIG. 12 is a schematic illustration of an electric motorcycle accordingto the third embodiment;

FIG. 13 is a schematic illustration of a rechargeable vacuum cleaneraccording to a fourth embodiment;

FIG. 14 is a constitution diagram of the rechargeable vacuum cleanershown in FIG. 13; and

FIG. 15 is a characteristic graph showing an example of a particlediameter distribution measured by laser diffraction in respect of amixture containing the first active material particles and second activematerial particles.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

The diffusion length of ions in the active material is shortened whenthe average particle diameter of the active material, which inserts andreleases lithium ions and in which the lithium diffusion coefficient is1×10⁻⁹ cm²/sec or less at 20° C., is 1 μm or less. As a result, outputperformance under a large load current is improved. However, theelectrode is heterogeneously impregnated with the nonaqueous electrolytesince the active material is too densely packed in the electrode. Also,contact between the active material and a current collector is impairedwhen an aluminum foil or aluminum alloy foil is used as a currentcollector of the active material particles. Consequently, the activematerial is peeled from the current collector by repeatingcharge-discharge cycle. For these reasons, high cycle performance couldnot be attained in the nonaqueous electrolyte battery that employsactive material particles having a lithium diffusion coefficient of1×10⁻⁹ cm²/sec or less at 20° C. and an average particle diameter of 1μm or less, and uses an aluminum foil or aluminum alloy foil as acurrent collector. The cycle performance was further decreased when thenonaqueous electrolyte battery was used in rechargeable vacuum cleanersand vehicles, since expansion and contraction of the active materialwere enhanced by subjecting the nonaqueous electrolyte battery to a deepcharge step and a deep discharge step repeatedly.

The inventors of the invention have found that the cycle performance ofthe nonaqueous electrolyte battery is improved when the nonaqueouselectrolyte battery satisfies the following conditions (a) and (b).

(a) The battery employs first active material particles that have anaverage particle diameter of 1 μm or less and in which the lithiumdiffusion coefficient is 1×10⁻⁹ cm²/sec or less at 20° C., and secondactive material particles having an average particle diameter in therange of 2 to 50 μm.

(b) The true density of the second active material particles is largerthan the true density of the first active material particles, and thedifference in the true densities between them is adjusted in the rangeof 0.01 to 2.5 g/cm³.

While the mechanism of the above-mentioned constitution for improvingthe cycle performance has not been elucidated yet, it may be conjecturedas follows. Since the second active material particles have a largeaverage particle diameter of 2 to 50 μm, spaces are formed in theelectrode and impregnating ability of the nonaqueous electrolyte isimproved. As a result, the contact area between the active material andnonaqueous electrolyte increases in the electrode, and thus diffusion oflithium ions in the electrode is improved due to increased an ionconductivity between the active material and nonaqueous electrolyte. Inaddition, the second active material particles readily sediment on thecurrent collector after coating the current collector with a slurrycontaining the first active material particles and second activematerial particles, when the true density of the first active materialparticles and second active material particles satisfies the condition(b). Consequently, the current collector is able to tightly adhere tothe active material layer and electronic conductivity of the electrodeis improved. Meanwhile, diffusion ability of lithium ions in theelectrode largely fluctuates by changing the average particle diameterfor the first active material particles having a lithium diffusioncoefficient of 1×10⁻⁹ cm²/sec or less at 20° C. The diffusion reactionof lithium ions has two stages of a solid state diffusion stage in theactive material particles and a liquid state diffusion stage in thenonaqueous electrolyte. The former is a rate-determining step in thefirst active material particles. Accordingly, diffusion ability oflithium ions in the electrode can be effectively improved by reducingthe average particle diameter of the active material particles, sincethe diffusion length of the lithium ion in the active material particlesis decreased by reducing the average particle diameter of the activematerial particles. On the other hand, fluctuation of diffusion abilityof lithium ions in the electrode is small in the lithium-cobaltcomposite oxide such as LiCoO₂ according to JP-A 2004-119218 even bychanging the average particle diameter, since the lithium diffusioncoefficient at 20° C. is larger than 1×10⁻⁹ cm²/sec.

The inventors of the invention have found that the active material layeris suppressed from being peeled from the current collector while a largeload current performance is improved, by improving adhesiveness betweenthe active material layer and the current collector, when the diffusionability of the lithium ion is largely dependent on the average particlediameter of the active material particles. Consequently, the battery issuppressed from being deteriorated by the charge-discharge cycle toenable the cycle performance to be improved. Improvement of the cycleperformance may be considered to be a result of a synergic effectbrought about by the improvements of electronic conductivity anddiffusion ability of the lithium ion in a good balance.

While cycle performance of the nonaqueous electrolyte battery can beimproved by using an electrode that satisfies the conditions (a) and (b)for at least one of a positive electrode and a negative electrode, theelectrode is desirably used at least for the negative electrode in orderto obtain a sufficient effect.

The composition of the first active material particles is desirablyrepresented by Li_(4+x)Ti₅O₁₂ (x changes in the range of 0≦x≦3 by thecharge-discharge reaction) when the electrode is used for the negativeelectrode. Since Li_(4+x)Ti₅O₁₂ has low electric conductivity by itself,improvement of the battery performance becomes particularly evident whenthe average particle diameter is small. The lithium diffusioncoefficient at 20° C. in Li_(4+x)Ti₅O₁₂ is approximately in the order of1×10⁻¹² cm²/sec. The lower limit of the lithium diffusion coefficient inthe first active material particles can be adjusted to 1×10⁻¹⁵ cm²/sec.

While the second active material particles may be particles capable ofinserting and releasing lithium ions, the composition may be selectedfrom Li_(4+x)Ti₅O₁₂ (x changes in the range of 0≦x≦3 by thecharge-discharge reaction), MnO₂, FeS, FeS₂, CuO, Cu₄O(PO₄)₂, MoO₃ andTiO₂. The composition of the second active material particles is notrestricted to one kind, and plural kinds of the compositions may beused.

In the case where the electrode is used for the positive electrode,examples of the first active material particles and second activematerial particles include Li_(y)Mn₂O₄ (y changes in the range of 0≦y≦1by the charge-discharge reaction). The lithium diffusion coefficient inLi_(y)Mn₂O₄ at 20° C. is approximately in the order of 10⁻⁹ cm²/sec.

The method for measuring the lithium diffusion coefficient will bedescribed below. The lithium diffusion coefficient is estimated bycyclic voltammetry in this embodiment. The nonaqueous electrolytebattery is disassembled in a glove box in an argon atmosphere, and thepositive electrode and negative electrode are taken out of the battery.The exposed positive and negative electrodes are washed with methylethylcarbonate to extract the nonaqueous electrolyte impregnated in thepositive and negative electrodes. After drying the positive and negativeelectrodes in vacuum, each electrode is cut into pieces with a size of2×2 cm. One piece of the electrode cut from the positive electrode isused as a working electrode while one piece of the electrode cut fromthe negative electrode is used as a working electrode when the positiveelectrode or negative electrode is used for the measurement,respectively. When either the positive electrode or negative electrodeis used for the working electrode, lithium metal is used for a counterelectrode and a reference electrode to manufacture a cell of a threepole type. The electrolytic solution used is prepared by dissolvingLiClO₄ at 1 M concentration in a mixed solvent of ethylene carbonate(EC) and diethyl carbonate (DEC) in 1:1 volume ratio. Voltamogram ismeasured in a scanning range from 0.5 to 4.4 V vs. Li/Li+ at 20° C.using the cell of the three pole type obtained. Voltamogram is measuredat each scanning rate of 1, 3, 5, 10, 20, 30, 40 or 50 mV/sec. Areduction peak current at each scanning rate is read from thevoltamogram obtained, the current intensity is plotted against the rootsquare of the scanning rate, and a gradient of the line obtained iscalculated. Since the gradient of the line corresponds to2.71×10⁵n^(3/2)AD^(1/2)c in equation (2) below, the diffusioncoefficient D is calculated from the relation of this value and thegradient of the line:

Ip=2.71×10⁵ n ^(3/2) AD ^(1/2) c  (2)

where Ip is a reduction peak current [A], n is the number of reactionelectrons, A is the area (cm²) of the working electrode, D is thediffusion coefficient (cm²/sec) at 20° C., v is the scanning rate[mV/sec] and c is the concentration of the electrolytic solution (1 M inthis example).

The first active material particles and second active material particleswill be described in more detail below.

The average particle diameter of the first active material particles isadjusted to 1 μm or less for improving the output performance under alarge load current of the nonaqueous electrolyte battery. However,nonconformity tends to occur in the electrode manufactured using thefirst active material particles having the average particle diameter ofless than 0.5 μm, and mass-productivity may be adversely affected.Accordingly, the lower limit of the average particle diameter isdesirably 0.5 μm. A more preferable range of the average particlediameter of the first active material particles is 0.55 to 0.95 μm.

The effect for improving impregnating ability of the nonaqueouselectrolyte cannot be obtained when the average particle diameter of thesecond active material particles is less than 2 μm. On the other hand,output performance under a large load current may be adversely affectedwhen the average particle diameter is larger than 50 μm since the iondiffusion length in the active material particles becomes too long.Accordingly, the average particle diameter of the active materialparticles is more preferably in the range of 3 to 40 μm.

The method for measuring the average particle diameter of the firstactive material particles and second active material particles will bedescribed below. The nonaqueous electrolyte battery is disassembled in aglove box in an argon atmosphere, and the positive electrode andnegative electrode are taken out of the battery. The exposed positiveelectrode and negative electrode are washed with methylethyl carbonateto extract the nonaqueous electrolyte impregnated in the positiveelectrode and negative electrode. After drying these electrodes invacuum, the positive electrode and negative electrode are independentlyimmersed in an N-methyl-2-pyrrolidone solution to extract a binder inthe positive electrode and negative electrode with theN-methyl-2-pyrrolidone solution. As a result, the active material layeris peeled from the current collector in the N-methyl-2-pyrrolidonesolution, and a powder mainly consisting of the first active materialparticles and second active material particles are dispersed in thesolution. The average particle diameter is measured by analyzing thesuspension with a laser diffraction particle size analyzer (for example,trade name: Micro Track MT 3200, manufactured by Nikkiso Co., Ltd.). Anexample of the particle diameter distribution measured by the laserdiffraction is shown in FIG. 15. The average particle diameter definedin the specification denotes a d50% value in the particle diameterdistribution.

An effect for improving the cycle performance cannot be obtained whenthe difference between the true density of the first active materialparticles and that of the second active material particles is smallerthan 0.01 g/cm³. On the other hand, an effect for improving impregnatingability of the liquid nonaqueous electrolyte by forming pores in theelectrode can be hardly obtained when the difference in the true densityis larger than 2.5 g/cm³ since the second active material particles aretoo concentrated on the current collector. Accordingly, the differencein the true density is more preferably in the range of 0.02 to 2 g/cm³.

The true density is a theoretical density for a solid material definedby taking atom deficiency, dislocations and trace impurities intoconsideration without taking pores in the solid material intoconsideration. Accordingly, means for adjusting the true density of theactive material particles include addition of trace impurities,adjustment of the oxygen content by controlling the atmosphere duringbaking, and setting of the baking condition (temperature or time).

The method for measuring the true density of the active materialparticles will be described below. A pycnometer method is used for themeasurement, while methanol is used for immersion liquid at roomtemperature (25° C.). About 10 to 15 g of the active material particlesare sampled in a pycnometer of 50 cc, the immersion liquid is filledtherein so that the active material particles are soaked with theimmersion liquid, and the immersion liquid is degassed in vacuum forabout 10 minutes. After degassing, the pycnometer is allowed to standfor 15 hours in a shaker equipped with a temperature controller set atroom temperature, and the density is determined by filling thepycnometer with the immersion liquid and measuring the weight.

While two peaks are observed in the particle size distribution measuredby the laser diffraction in respect of the mixture containing the firstactive material particles and the second active material particles, thefirst peak and second peak desirably satisfy equation (1) below providedthat the peak at a smaller particle diameter corresponds to the firstpeak and the peak at the larger particle diameter corresponds to thesecond peak:

2≦(F ₁ /F ₂)≦20  (1)

where F₁ is the frequency of the first peak and F₂ is the frequency ofthe second peak.

The first peak may be considered as a mode diameter in the particlediameter distribution measured by the laser diffraction in respect ofthe first active material particles, while the second peak may beconsidered as a mode diameter in the particle diameter distribution ofthe second active material particles. The mode diameter as used hereindenotes a peak top of the particle diameter distribution by providing ahorizontal axis for the particle diameter and a vertical axis for thefrequency, which distribution is measured by the laser diffraction.Accordingly, the ratio of F₁/F₂ may be used as an index of theproportion of the first active material particles to the second activematerial particles. A F₁/F₂ ratio of 2 or more permits the outputperformance under a large load current to be improved since the specificsurface area of the electrode can be sufficiently increased. The cycleperformance may be further improved by adjusting the F₁/F₂ ratio to 20or less. The F₁/F₂ ratio is more preferably in the range of 5 to 15.

The frequencies of the first and second peaks are calculated using theparticle diameter distribution measured by the laser diffraction asshown in FIG. 15. There are two peaks in the particle diameterdistribution in FIG. 15. A first peak A at the smaller particle diametercan be considered as the mode diameter of the first active materialparticles. The frequency F₁ of the first peak A is 5.53% in FIG. 15. Asecond peak B at the larger particle diameter can be considered as themode diameter of the second active material particles. The frequency F₂of the second peak B is 0.80% in FIG. 15. Accordingly, the F₁/F₂ ratiois 6.91 in FIG. 15.

The specific surface area of the first active material particles isdesirably in the range of 7 to 100 m²/g. Impregnating ability of thenonaqueous electrolyte may be further improved when the specific surfacearea is 7 m²/g or more. In addition, side reactions due to an increaseof reaction fields may be suppressed when the specific surface area is100 m²/g or less. The specific surface area of the first active materialparticles is more preferably in the range of 8 to 40 m²/g.

The nonaqueous electrolyte battery according to the invention will bedescribed below for respective parts.

(1) Positive Electrode

The positive electrode comprises a positive electrode current collectorand a positive electrode active material layer that is laminated on onesurface or both surfaces of the current collector and contains an activematerial, a conductive agent and a binder. The positive electrode ismanufactured, for example, by adding the conductive agent and binder tothe positive electrode active material, suspending them in anappropriate solvent, and applying the slurry on the current collectorfollowed by drying and pressing to form a strip-shaped electrode.

While the above-mentioned first active material particles and secondactive material particles can be used for the positive electrode activematerial, a positive electrode active material other than the activematerial comprising the first active material particles and secondactive material particles may be used when the above-mentioned firstactive material particles and second active material particles are usedfor the negative electrode active material.

Examples of the positive electrode active material other than the activematerial comprising the first active material particles and secondactive material particles include manganese dioxide (MnO₂), iron oxide,copper oxide, nickel oxide, Li_(a)MnO₂, lithium-nickel composite oxide(for example Li_(a)NiO₂), lithium-cobalt composite oxide (for exampleLi_(a)CoO₂), lithium-nickel-cobalt composite oxide {for exampleLiNi_(1-e-f)Co_(e)M_(f)O₂ (M is at least one element selected from thegroup consisting of Al, Cr and Fe), 0≦e≦0.5, 0≦f≦0.1},lithium-manganese-cobalt composite oxide {for exampleLiMn_(1-g-h)Co_(g)M_(h)O₂ (M is at least one element selected from thegroup consisting of Al, Cr and Fe), 0≦g≦0.5, 0≦h≦0.1},lithium-manganese-nickel composite oxide {for exampleLiMn_(j)Ni_(j)M_(1-2j)O₂ (M is at least one element selected from thegroup consisting of Co, Cr, Al and Fe), ⅓≦j≦½, for exampleLiMn_(1/3)Ni_(1/3)Co_(1/3)O₂, LiMn_(1/2)Ni_(1/2)O₂}, spinel typelithium-manganese-nickel composite oxide (Li_(a)Mn_(2-b)Ni_(b)O₄),lithium iron phosphates having an olivine structure (such asLi_(a)FePO₄, Li_(a)Fe_(1-b)Mn_(b)PO₄ and Li_(a)CoPO₄), iron sulfate(Fe₂(SO₄)₃), and vanadium oxide (for example V₂O₅). A preferable rangeof a, b and c is 0 to 1. Examples of other materials include organic andinorganic materials. Examples of the organic and inorganic materialsinclude conductive polymer materials such as polyaniline andpolypyrrole, disulfide polymer materials, sulfur (S) and fluorinatedcarbon.

Examples of more preferable positive electrode active materials includelithium-nickel composite oxide, lithium-cobalt composite oxide,lithium-nickel-cobalt composite oxide, lithium-manganese-nickelcomposite oxide, spinel type lithium-manganese-nickel composite oxide,lithium-manganese-cobalt composite oxide and lithium iron phosphates.These positive electrode active materials afford a high battery voltage.

Examples of the conductive agent include acetylene black, KETJEN BLACK,graphite and coke.

Examples of the binder include polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVdF) and fluorinated rubber.

Preferably, the blending ratio of the positive electrode active materialis in the range of 80 to 95% by weight, the blending ratio of theconductive agent is in the range of 3 to 20% by weight, and the blendingratio of the binder is in the range of 2 to 7% by weight.

It is desirable for the positive electrode current collector to beformed of an aluminum foil or an aluminum alloy foil. It is desirablefor the aluminum foil or the aluminum alloy foil forming the positiveelectrode current collector to have an average crystal grain size notlarger than 50 μm. It is more desirable for the average crystal grainsize noted above to be not larger than 30 μm, and furthermore desirablynot larger than 5 μm. Where the average crystal grain size of thealuminum foil or the aluminum alloy foil forming the positive electrodecurrent collector is not larger than 50 μm, the mechanical strength ofthe aluminum foil or the aluminum alloy foil can be drasticallyincreased to make it possible to press the positive electrode with ahigh pressure. It follows that the density of the positive electrode canbe increased to increase the battery capacity.

The average crystal grain size can be obtained as follows. Specifically,the texture of the current collector surface is observed with anelectron microscope so as to obtain the number n of crystal grainspresent within an area of 1 mm×1 mm. Then, the average crystal grainarea S is obtained from the formula “S=1×10⁶/n (μm²)”, where n is thenumber of crystal grains noted above. Further, the average crystal grainsize d (μm) is calculated from the area S by formula (A) given below:

d=2(S/π)^(1/2)  (A)

The average crystal grain size of the aluminum foil or the aluminumalloy foil can be complicatedly affected by many factors such as thecomposition of the material, the impurities, the process conditions, thehistory of the heat treatments and the heating conditions such as theannealing conditions, and the crystal grain size can be adjusted by anappropriate combination of the factors noted above during themanufacturing process.

It is desirable for the aluminum foil or the aluminum alloy foil to havea thickness not larger than 20 μm, preferably not larger than 15 μm.Also, it is desirable for the aluminum foil to have a purity not lowerthan 99%. Further, it is desirable for the aluminum alloy to contain,for example, magnesium, zinc and silicon. On the other hand, it isdesirable for the content of the transition metals such as iron, copper,nickel and chromium in the aluminum alloy to be not higher than 1%.

(2) Negative Electrode

The negative electrode comprises a negative electrode current collectorand a negative electrode active material layer that is laminated on onesurface or both surfaces of the current collector and contains an activematerial, a binder and optionally a conductive agent. The negativeelectrode is manufactured, for example, by adding the binder to a powderof the negative electrode active material, suspending them in anappropriate solvent, and applying the slurry on the current collectorfollowed by drying and pressing to form a strip-shaped electrode.

While the above-mentioned first active material particles and secondactive material particles may be used for the negative electrode activematerial, a negative electrode active material other than the activematerial comprising the first active material particles and secondactive material particles may be used when the above-mentioned firstactive material particles and second active material particles are usedfor the positive electrode active material.

Examples of the negative electrode active material other than the activematerial comprising the first active material particles and secondactive material particles include lithium metal, lithium alloy,carbonaceous material and metal compounds.

Examples of the lithium alloy include lithium-aluminum alloy,lithium-zinc alloy, lithium-magnesium alloy, lithium-silicon alloy andlithium-lead alloy. A lithium alloy foil may be directly used as astrip-shaped electrode.

Examples of the carbonaceous material include natural graphite,synthetic graphite, coke, vapor-grown carbon fiber, mesophase pitchbased carbon fiber, spherical carbon and resin-baked carbon. Preferableexamples of the carbonaceous material include vapor-grown carbon fiber,mesophase pitch based carbon fiber and spherical carbon. Thecarbonaceous material preferably has a layer spacing d₀₀₂ of 0.340 nm orless derived from (002) reflection of X-ray diffraction.

Examples of the metal compound include metal oxide, metal sulfide andmetal nitride.

Examples of the above-mentioned metal oxide include titanium-containingmetal composite oxide, amorphous tin oxide such asSnB_(0.4)P_(0.6)O_(3.1), tin silicates such as SnSiO₃, silicon oxidesuch as SiO and tungsten oxide such as WO₃. The titanium-containingmetal composite oxide is preferable among them.

Examples of the titanium-containing metal composite oxide includeLi_(2+f)Ti₃O₇ (−1≦f≦3) having a ramsdelite structure, and metalcomposite oxide containing Ti and at least one element selected from thegroup consisting of P, V, Sn, Cu, Ni and Fe. Examples of the metalcomposite oxide, containing Ti and at least one element selected fromthe group consisting of P, V, Sn, Cu, Ni and Fe, include TiO₂—P₂O₅,TiO₂-V₂O₅, TiO₂—P₂O₅—SnO₂ and TiO₂—P₂O₅—MeO (Me is at least one elementselected from the group consisting of Cu, Ni and Fe). The metalcomposite oxide preferably has low crystallinity and a micro-structurecomprising a crystalline phase and an amorphous phase together or theamorphous phase alone. Such micro-structure permits the cycleperformance to be largely improved. The lithium-titanium oxide and metalcomposite oxide containing Ti and at least one element selected from thegroup consisting of P, V, Sn, Cu, Ni and Fe are preferable among them.

Examples of the metal sulfide include titanium sulfide such as TiS₂,molybdenum sulfide such as MoS₂ and iron sulfide such as FeS, FeS₂ andLi_(x)FeS₂.

Examples of the metal nitride include lithium-cobalt nitride (forexample Li_(s)Co_(t)N, 0<s<4, 0<t<0.5).

Examples of the conductive agent include acetylene black, KETJEN BLACK,graphite and metal powder.

Examples of the binder include polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVdF), fluorinated rubber and styrene-butadienerubber.

Preferably, the blending ratio of the negative electrode active materialis in the range of 80 to 98% by weight, the blending ratio of theconductive agent is in the range of 0 to 20% by weight, and the blendingratio of the binder is in the range of 2 to 7% by weight.

It is desirable for the current collector of the negative electrode tobe formed of aluminum foil or aluminum alloy foil. It is also desirablefor the negative electrode current collector to have an average crystalgrain size not larger than 50 μm. In this case, the mechanical strengthof the current collector can be drastically increased so as to make itpossible to increase the density of the negative electrode by applyingthe pressing under a high pressure to the negative electrode. As aresult, the battery capacity can be increased. Also, since it ispossible to prevent the dissolution, corrosion and deterioration of thenegative electrode current collector in an over-discharge cycle under anenvironment of a high temperature not lower than, for example, 40° C.,it is possible to suppress the elevation in the impedance of thenegative electrode. Further, it is possible to improve the outputperformance, the rapid charging performance, and the charge-dischargecycle performance of the battery. It is more desirable for the averagecrystal grain size of the negative electrode current collector to be notlarger than 30 μm, furthermore desirably, not larger than 5 μm.

It is desirable for the aluminum foil or the aluminum alloy foil to havea thickness not larger than 20 μm, more desirably not larger than 15 μm.Also, it is desirable for the aluminum foil to have a purity not lowerthan 99%. It is desirable for the aluminum alloy to contain anotherelement such as magnesium, zinc or silicon. On the other hand, it isdesirable for the amount of the transition metal such as iron, copper,nickel and chromium contained in the aluminum alloy to be not largerthan 1%.

(3) Nonaqueous Electrolyte

The nonaqueous electrolyte contains a nonaqueous solvent and anelectrolyte dissolved in the nonaqueous solvent. The nonaqueous solventcan contain a polymer.

Examples of the electrolyte include lithium salts such as LiPF₆, LiBF₄,Li(CF₃SO₂)₂N (bis-trifluoromethane-sulfonylamide lithium; common nameLiTFSI), LiCF₃SO₃ (common name LiTFS), Li(C₂F₅SO₂)₂N(bis-pentafluoroethanesulfonyl-amide lithium; common name LiBETI),LiClO₄, LiAsF₆, LiSbF₆, lithium bis-oxalatoborate (LiB(C₂O₄)₂, commonname LiBOB), anddifluoro(trifluoro-2-oxide-2-trifluoro-methylpropionate(2-)-0,0) lithiumborate (LiBF₂(OCOOC(CF₃)₂), (common name LiBF₂(HHIB))). One of theseelectrolyte may be used alone, or by mixing a plurality of them. LiPF₆and LiBF₄ are particularly preferable.

The concentration of the electrolyte is preferably in the range of 1.5to 3 M. In this manner, the performance under a large load current isfurther improved while the nonaqueous electrolyte is suppressed frombeing affected by the increase of the viscosity due to the increase ofthe electrolyte concentration.

While the nonaqueous solvent is not particularly restricted, examples ofthe solvent include propylene carbonate (PC), ethylene carbonate (EC),1,2-dimethoxyethane (DME), γ-butyrolactone (GBL), tetrahydrofuran (THF),2-methyl tetrahydrofuran (2-MeHF), 1,3-dioxolane, sulfolane,acetonitrile (AN), diethyl carbonate (DEC), dimethyl carbonate (DMC),methylethyl carbonate (MEC) and dipropyl carbonate (DPC). One of thesesolvents may be used alone, or a plurality of them may be used bymixing. γ-butyrolactone is preferable among them when thermal stabilityis emphasized. The solvent preferably contains EC, PC and GBL whenthermal stability as well as low temperature performance is necessary.The thermal stability and the low temperature performance considered asthe result of increase of entropy may be expected to increase byallowing the solvent to contain EC, PC and GBL as the cyclic carbonates.Since the cyclic carbonate has a larger viscosity than a linearcarbonate, the cycle performance may be largely improved by using anonaqueous solvent consisting essentially of the cyclic carbonatesaccording to this embodiment.

Additives may be added to the nonaqueous electrolyte. While the additiveis not particularly restricted, examples of the additive includevinylene carbonate (VC), vinylene acetate (VA), vinylene butyrate,vinylene hexanate, vinylene crotonate, and catechol carbonate. Theconcentration of the additive is preferably in the range of 0.1 to 3 wt%, more preferably 0.5 to 1 wt %, relative to 100 wt % of the nonaqueouselectrolyte.

The structure of the nonaqueous electrolyte battery according to thefirst embodiment is not particularly restricted, and may be variousstructures such as a flat structure, a rectangular structure and acylindrical structure. An example of the flat nonaqueous electrolytebattery is shown in FIGS. 1 to 3.

As shown in FIG. 1, an electrode group 1 has a structure in which apositive electrode 2 and a negative electrode 3 are coiled in a flatshape with interposition of a separator 4 between the electrodes. Theelectrode group 1 is manufactured by applying hot-press after coilingthe positive electrode 2 and negative electrode 3 with interposition ofthe separator 4 therebetween. The positive electrode 2, negativeelectrode 3 and separator 4 in the electrode group 1 may be integratedwith an adhesive polymer. A belt-like positive electrode terminal 5 iselectrically connected to the positive electrode 2, while a belt-likenegative electrode terminal 6 is electrically connected to the negativeelectrode 3. The electrode group 1 is housed in a laminate film case 7having heat-seal portions on three edges. The tips of the positiveelectrode terminal 5 and negative electrode terminal 6 are pulled outfrom the shorter edge of the heat seal portion of the case 7.

While the tips of the positive electrode terminal 5 and negativeelectrode terminal 6 are pulled out from the same heat seal portion(seal portion) of the case 7, the heat seal portion from which thepositive electrode terminal 5 is pulled out may be different from theheat seal portion from which the negative electrode terminal 6 is pulledout. A specific example of the structure is shown in FIGS. 2 and 3.

As shown in FIG. 2, a laminated electrode group 8 is housed in the case7 made of the laminate film. As show in FIG. 3, the laminate filmcomprises, for example, a resin layer 10, a thermoplastic resin layer11, and a metal layer 9 disposed between the resin layer 10 andthermoplastic resin layer 11. The thermoplastic resin layer 11 islocated on the inner surface of the case 7. Heat-seal portions 7 a, 7 band 7 c are formed by thermal adhesion of the thermoplastic resin layer11 at one longer edge and both shorter edges of the case 7 made of thelaminate film. The case 7 is sealed with the heat-seal portions 7 a, 7 band 7 c. The laminated electrode group 8 has a structure in which thepositive electrodes 2 and negative electrodes 3 are alternatelylaminated with interposition of the separators 4 between them. Pluralpositive electrodes 2 are used, and each electrode comprises a positiveelectrode current collector 2 a and positive electrode active materiallayers 2 b laminated on both surfaces of the positive electrode currentcollector 2 a. Plural negative electrodes 3 are used, and each electrodecomprises a negative electrode current collector 3 a and negativeelectrode active material layers 3 b laminated on both surfaces of thenegative electrode current collector 3 a. One edge of the negativeelectrode current collector 3 a of the negative electrode 3 is protrudedout of the positive electrode 2. The negative electrode currentcollector 3 a protruded out of the positive electrode 2 is electricallyconnected to the belt-like negative electrode terminal 6. The tip of thebelt-like negative electrode terminal 6 is pulled out to the outsidethrough the heat seal portion 7 c of the case 7. Both surfaces of thenegative electrode terminal 6 are opposed to the thermoplastic resinlayers 11 that constitute the heat seal portion 7 c. An insulation film12 is inserted between each surface of the negative electrode terminal 6and the thermoplastic resin layer 11 for improving the bonding strengthbetween the heat seal portion 7 c and the negative electrode terminal 6.An example of the insulation film 12 is a film formed of a materialprepared by adding an acid anhydride to a polyolefin that contains atleast one of polypropylene and polyethylene. The edge of the positiveelectrode current collector 2 a of the positive electrode 2 is protrudedout of the negative electrode 3, although this configuration is notillustrated in the drawing. The edge of the positive electrode currentcollector 2 a is positioned at an opposed side to the protruded edge ofthe negative electrode current collector 3 a, The positive electrodecurrent collector 2 a protruded out of the negative electrode 3 iselectrically connected to the belt-like positive electrode terminal 5.The tip of the belt-like positive electrode terminal 5 is pulled outthrough the heat seal portion 7 b of the case 7. The insulation film 12is interposed between the positive electrode terminal 5 and thethermoplastic resin layer 11 for improving bonding strength between theheat seal portion 7 b and the positive electrode terminal 5. Thedirection in which the positive electrode terminal 5 is pulled out ofthe case 7 is opposed to the direction in which the negative electrodeterminal 6 is pulled out of the case 7, as is evident from theabove-described construction.

As shown in FIGS. 2 and 3, a nonaqueous electrolyte battery favorablefor use under a large load current may be provided by providing thepull-out direction of the positive electrode terminal 5 so as to beopposed to the pull-out direction of the negative electrode terminal 6.

The positive electrode terminal, the negative electrode terminal and thecase will be described below.

The positive electrode terminal may be formed of a conductive materialhaving electric stability at the potential with respect to the lithiummetal in the range of 3 to 5 V. Specific examples of the materialinclude aluminum alloys containing Mg, Ti, Zn, Mn, Fe, Cu or Si. Thesame material as that of the positive electrode current collector ispreferably used for the positive electrode terminal for reducing contactresistance.

The negative electrode terminal may be formed of a conductive materialhaving electric stability at the potential with respect to the lithiummetal in the range of 0.4 to 3 V. Specific examples of the materialinclude aluminum alloys containing Mg, Ti, Zn, Mn, Fe, Cu or Si. Thesame material as that of the negative electrode current collector ispreferably used for the negative electrode terminal for reducing contactresistance.

A multilayer film comprising a metal foil covered with a resin film maybe used for the laminate film constituting the case. The resin availableincludes polymer films such as polypropylene (PP) film, polyethylene(PE) film, nylon film or polyethylene terephthalate (PET) film. As shownin FIG. 2 above, polypropylene (PP) or polyethylene (PE) may be used asa thermoplastic resin when one of the resin films is formed of thethermoplastic resin. The metal foil can be formed of aluminum or analuminum alloy. The thickness of the laminate film is desirably 0.2 mmor less.

While the case made of the laminate film is used in FIGS. 1 to 3, thematerial of the case is not particularly restricted and, for example, acase made of a metal with a thickness of 0.5 mm or less may be used. Themetal case available is a rectangular or cylindrical metal can made ofaluminum, an aluminum alloy, iron or stainless steel. The thickness ofthe metal case is desirably 0.2 mm or less.

The aluminum alloy constituting the metal case is preferably an alloycontaining elements such as magnesium, zinc and silicon. However, thecontent of transition metals such as iron, copper, nickel and chromiumis preferably 1% or less. This composition permits long term reliabilityunder a high temperature environment and heat dissipating ability to beremarkably improved.

The metal can made of aluminum or an aluminum alloy preferably has anaverage crystal grain size of 50 μm or less, more preferably 30 μm orless, and further preferably 5 μm or less. The strength of the metal canmade of aluminum or an aluminum alloy can be remarkably increased bycontrolling the average crystal grain size to be 50 μm or less to enablethe can to be thin. Consequently, a vehicle-mounted battery that islight weight, shows high output power and is excellent in long termreliability can be realized.

Examples of the electrode group is the coiled structure shown in FIG. 1,or the laminate structure shown in FIGS. 2 and 3. The structure of theelectrode group is preferably a laminated structure in order to endowthe battery with excellent input-output characteristics as well as highsafety and reliability. The electrode group including the positiveelectrode and negative electrode preferably has a laminated structure inwhich the separator is used by folding it into a zigzag shape as shownin FIG. 4 for improving a large load current performance during a longterm use. The strip-shaped separator 4 is also folded into a zigzagshape. A strip 3 ₁ of the negative electrode is laminated on theuppermost layer of the separator 4 folded into a zigzag shape. A strip 2₁ of the positive electrode, a strip 3 ₂ of the negative electrode, astrip 2 ₂ of the positive electrode and a strip 3 ₃ of the negativeelectrode are sequentially inserted into the respective overlap portionsof the separators 4 from the top in this order. The electrode grouphaving the laminated structure is obtained by alternately disposing thepositive electrodes 2 and negative electrodes 3 between the separators 4folded into a zigzag shape.

The nonaqueous electrolyte can be smoothly supplied to the electrode byfolding the separator into a zigzag shape since respective three edgesof the positive electrode and negative electrode are able to directlycontact the nonaqueous electrolyte without intervention of theseparator. Accordingly, the nonaqueous electrolyte is smoothly suppliedto the electrode even when the nonaqueous electrolyte is consumed on thesurface of the electrode during a long term use, and excellent largeload current characteristics (input-output characteristics) may berealized for a long period of time.

Second Embodiment

A battery pack according to a second embodiment comprises a plurality ofnonaqueous electrolyte batteries according to the first embodiment. Thenonaqueous electrolyte battery of the first embodiment is used as a unitcell, and the plural unit cells are desirably connected in series or inparallel to construct a battery module.

The nonaqueous electrolyte battery of the first embodiment is suitablefor use as the battery module, while the battery pack of the secondembodiment is excellent in cycle performance. These embodiments will bedescribed below.

The surface of the active material can easily come in contact with thenonaqueous electrolyte by improving impregnating ability of thenonaqueous electrolyte at the positive or negative electrode, and thelithium ion concentration in the active material can be readily evened.Consequently, the unit cell hardly suffers from over-voltage, namely,the active material can be evenly utilized since local over-charge andover-discharge hardly occur. Therefore, individual difference of thecapacity of the unit cell and individual difference of impedance can bereduced. As a result, fluctuation of the voltage of the unit cell at afully charged state due to individual difference of the capacity can bereduced, for example, in the battery module in which the unit cells areconnected in series. Accordingly, the battery pack of the secondembodiment is excellent in controllability of the battery module withimproved cycle performance.

Each of a plurality of unit cells 21 included in the battery pack shownin FIG. 5 is formed of, though not limited to, a flattened typenonaqueous electrolyte battery constructed as shown in FIG. 1. It ispossible to use the flattened type nonaqueous electrolyte battery shownin FIGS. 2 and 3 as the unit cell 21. The plural unit cells 21 arestacked one upon the other in the thickness direction in a manner toalign the protruding directions of the positive electrode terminals 5and the negative electrode terminals 6. As shown in FIG. 6, the unitcells 21 are connected in series to form a battery module 22. The unitcells 21 forming the battery module 22 are made integral by using anadhesive tape 23 as shown in FIG. 5.

A printed wiring board 24 is arranged on the side surface of the batterymodule 22 toward which protrude the positive electrode terminals 5 andthe negative electrode terminals 6. As shown in FIG. 6, a thermistor 25,a protective circuit 26 and a terminal 27 for current supply to theexternal equipment are connected to the printed wiring board 24.

As shown in FIGS. 5 and 6, a wiring 28 on the side of the positiveelectrodes of the battery module 22 is electrically connected to aconnector 29 on the side of the positive electrode of the protectivecircuit 26 mounted to the printed wiring board 24. On the other hand, awiring 30 on the side of the negative electrodes of the battery module22 is electrically connected to a connector 31 on the side of thenegative electrode of the protective circuit 26 mounted to the printedwiring board 24.

The thermistor 25 detects the temperature of the unit cell 21 andtransmits the detection signal to the protective circuit 26. Theprotective circuit 26 is capable of breaking a wiring 31 a on thepositive side and a wiring 31 b on the negative side, the wirings 31 aand 31 b being stretched between the protective circuit 26 and theterminal 27 for current supply to the external equipment. These wirings31 a and 31 b are broken by the protective circuit 26 under prescribedconditions including, for example, the conditions that the temperaturedetected by the thermistor is higher than a prescribed temperature, andthat the over-charging, over-discharging and over-current of the unitcell 21 have been detected. The detecting method is applied to the unitcells 21 or to the battery module 22. In the case of applying thedetecting method to each of the unit cells 21, it is possible to detectthe battery voltage, the positive electrode potential or the negativeelectrode potential. On the other hand, where the positive electrodepotential or the negative electrode potential is detected, lithium metalelectrodes used as reference electrodes are inserted into the unit cells21.

In the case of FIG. 6, a wiring 32 is connected to each of the unitcells 21 for detecting the voltage, and the detection signal istransmitted through these wirings 32 to the protective circuit 26.

Protective sheets 33 each formed of rubber or resin are arranged on thethree of the four sides of the battery module 22, though the protectivesheet 33 is not arranged on the side toward which protrude the positiveelectrode terminals 5 and the negative electrode terminals 6. Aprotective block 34 formed of rubber or resin is arranged in theclearance between the side surface of the battery module 22 and theprinted wiring board 24.

The battery module 22 is housed in a container 35 together with each ofthe protective sheets 33, the protective block 34 and the printed wiringboard 24. To be more specific, the protective sheets 33 are arrangedinside the two long sides of the container 35 and inside one short sideof the container 35. On the other hand, the printed wiring board 24 isarranged along that short side of the container 35 which is opposite tothe short side along which one of the protective sheets 33 is arranged.The battery module 22 is positioned within the space surrounded by thethree protective sheets 33 and the printed wiring board 24. Further, alid 36 is mounted to close the upper open edge of the container 35.

Incidentally, it is possible to use a thermally shrinkable tube in placeof the adhesive tape 23 for fixing the battery module 22. In this case,the protective sheets 33 are arranged on both sides of the batterymodule 22 and, after the thermally shrinkable tube is wound about theprotective sheets, the tube is thermally shrunk to fix the batterymodule 22.

The unit cells 21 shown in FIGS. 5 and 6 are connected in series.However, it is also possible to connect the unit cells 21 in parallel toincrease the cell capacity. Of course, it is possible to connect thebattery packs in series and in parallel.

Also, the embodiments of the battery pack can be changed appropriatelydepending on the use of the battery pack.

The battery pack according to the second embodiment is preferably usedwhen good cycle performance is required at a large load current (highcurrent density). Specifically, the battery pack is used for powersources of digital cameras, vehicle-mounted batteries for two-wheel orfour-wheel hybrid electric cars, two-wheel or four-wheel electric carsand electric mopeds, and power sources of rechargeable vacuum cleaners.Since the battery pack according to this embodiment has a high effectfor preventing the active material layer from being peeled from thecurrent collector due to expansion and contraction resulting from cyclesof deep charge and deep discharge, the battery pack is suitable for usein the rechargeable vacuum cleaner and vehicle.

Third Embodiment

A vehicle according to a third embodiment of the present inventioncomprises the battery pack according to the second embodiment. Thevehicle noted above includes, for example, a hybrid electric automobilehaving 2 to 4 wheels, an electric automobile having 2 to 4 wheels, andan electric moped.

FIGS. 7 to 9 show various type of hybrid vehicles in which an internalcombustion engine and a motor driven by a battery pack are used incombination as the power source for the driving. For driving thevehicle, required is the power source exhibiting a wide range of therotation speed and the torque depending on the running conditions of thevehicle. Since the torque and the rotation speed exhibiting an idealenergy efficiency are limited in the internal combustion engine, theenergy efficiency is lowered under the driving conditions other than thelimited torque and the rotation speed. Since the hybrid vehicle includesthe internal combustion engine and the electric motor, it is possible toimprove the energy efficiency of the vehicle. Specifically, the internalcombustion engine is operated under the optimum conditions so as togenerate an electric power, and the wheels are driven by ahigh-efficiency electric motor, or the internal combustion engine andthe electric motor are operated simultaneously, thereby improving theenergy efficiency of the vehicle. Also, by recovering the kinetic energyof the vehicle in the decelerating stage as the electric power, therunning distance per unit amount of the fuel can be drasticallyincreased, compared with the vehicle that is driven by the internalcombustion engine alone.

The hybrid vehicle can be roughly classified into three types dependingon the combination of the internal combustion engine and the electricmotor.

FIG. 7 shows a hybrid vehicle 50 that is generally called a serieshybrid vehicle. The motive power of an internal combustion engine 51 isonce converted entirely into an electric power by a power generator 52,and the electric power thus converted is stored in a battery pack 54 viaan inverter 53. The battery pack according to the second embodiment isused as the battery pack 54. The electric power stored in the batterypack 54 is supplied to an electric motor 55 via the inverter 53, withthe result that wheels 56 are driven by the electric motor 55. In otherwords, the hybrid vehicle 50 shown in FIG. 7 represents a system inwhich a power generator is incorporated into an electric vehicle. Theinternal combustion engine can be operated under highly efficientconditions and the kinetic energy of the internal combustion engine canbe recovered as the electric power. On the other hand, the wheels aredriven by the electric motor alone and, thus, the hybrid vehicle 50requires an electric motor of a high output. It is also necessary to usea battery pack having a relatively large capacity. It is desirable forthe rated capacity of the battery pack to fall within a range of 5 to 50Ah, more desirably 10 to 20 Ah. Incidentally, the rated capacity notedabove is the capacity at the time when the battery pack is discharged ata rate of 0.2C.

FIG. 8 shows the construction of a hybrid vehicle 57 that is called aparallel hybrid vehicle. A reference numeral 58 shown in FIG. 8 denotesan electric motor that also acts as a power generator. The internalcombustion engine 51 drives mainly the wheels 56. The motive power ofthe internal combustion engine 51 is converted in some cases into anelectric power by the power generator 58, and the battery pack 54 ischarged by the electric power produced from the power generator 58. Inthe starting stage or the accelerating stage at which the load isincreased, the driving force is supplemented by the electric motor 58.The hybrid vehicle 57 shown in FIG. 8 represents a system based on theordinary vehicle. In this system, the fluctuation in the load of theinternal combustion engine 51 is suppressed so as to improve theefficiency, and the regenerative power is also obtained. Since thewheels 56 are driven mainly by the internal combustion engine 51, theoutput of the electric motor 58 can be determined arbitrarily dependingon the required ratio of the assistance. The system can be constructedeven in the case of using a relatively small electric motor 58 and arelatively small battery pack 54. The rated capacity of the battery packcan be set to fall within a range of 1 to 20 Ah, more desirably 5 to 10Ah.

FIG. 9 shows the construction of a hybrid vehicle 59 that is called aseries-parallel hybrid vehicle, which utilizes in combination both theseries type system and the parallel type system. A power dividingmechanism 60 included in the hybrid vehicle 59 divides the output of theinternal combustion engine 51 into the energy for the power generationand the energy for the wheel driving. The series-parallel hybrid vehicle59 permits controlling the load of the engine more finely than theparallel hybrid vehicle so as to improve the energy efficiency.

It is desirable for the rated capacity of the battery pack to fallwithin a range of 1 to 20 Ah, more desirably 5 to 10 Ah.

It is desirable for the nominal voltage of the battery pack included inthe hybrid vehicles as shown in FIGS. 7 to 9 to fall within a range of200 to 600 V.

The battery pack according to embodiments of the present invention isadapted for use in the series-parallel hybrid vehicle.

It is desirable for the battery pack 54 to be arranged in general in thesite where the battery pack 54 is unlikely to be affected by the changein the temperature of the outer atmosphere and unlikely to receive animpact in the event of a collision. In, for example, a sedan typeautomobile shown in FIG. 10, the battery pack 54 can be arranged withina trunk room rearward of a rear seat 61. The battery pack 54 can also bearranged below or behind the rear seat 61. Where the battery has a largeweight, it is desirable to arrange the battery pack 54 below the seat orbelow the floor in order to lower the center of gravity of the vehicle.

An electric vehicle (EV) is driven by the energy stored in the batterypack that is charged by the electric power supplied from outside thevehicle. Therefore, it is possible for the electric vehicle to utilizethe electric energy generated at a high efficiency by, for example,another power generating equipment. Also, since the kinetic energy ofthe vehicle can be recovered as the electric power in the deceleratingstage of the vehicle, it is possible to improve the energy efficiencyduring the driving of the vehicle. It should also be noted that theelectric vehicle does not discharge at all the waste gases such as acarbon dioxide gas and, thus, the air pollution problem need not beworried about at all. On the other hand, since all the power requiredfor the driving of the vehicle is produced by an electric motor, it isnecessary to use an electric motor of a high output. In general, it isnecessary to store all the energy required for one driving in thebattery pack by one charging. It follows that it is necessary to use abattery pack having a very large capacity. It is desirable for the ratedcapacity of the battery pack to fall within a range of 100 to 500 Ah,more desirably 200 to 400 Ah.

The weight of the battery pack occupies a large ratio of the weight ofthe vehicle. Therefore, it is desirable for the battery pack to bearranged in a low position that is not markedly apart from the center ofgravity of the vehicle. For example, it is desirable for the batterypack to be arranged below the floor of the vehicle. In order to allowthe battery pack to be charged in a short time with a large amount ofthe electric power required for the one driving, it is necessary to usea charger of a large capacity and a charging cable. Therefore, it isdesirable for the electric vehicle to be equipped with a chargingconnector connecting the charger and the charging cable. A connectorutilizing the electric contact can be used as the charging connector. Itis also possible to use a non-contact type charging connector utilizingthe inductive coupling.

FIG. 11 exemplifies the construction of a hybrid motor bicycle 63. It ispossible to construct a hybrid motor bicycle 63 exhibiting a high energyefficiency and equipped with an internal combustion engine 64, anelectric motor 65, and the battery pack 54 like the hybrid vehicle. Theinternal combustion engine 64 drives mainly the wheels 66. In somecases, the battery pack 54 is charged by utilizing a part of the motivepower generated from the internal combustion engine 64. In the startingstage or the accelerating stage in which the load of the motor bicycleis increased, the driving force of the motor bicycle is supplemented bythe electric motor 65. Since the wheels 66 are driven mainly by theinternal combustion engine 64, the output of the electric motor 65 canbe determined arbitrarily based on the required ratio of the supplement.The electric motor 65 and the battery pack 54, which are relativelysmall, can be used for constructing the system. It is desirable for therated capacity of the battery pack to fall within a range of 1 to 20 Ah,more desirably 3 to 10 Ah.

FIG. 12 exemplifies the construction of an electric motor bicycle 67.The electric motor bicycle 67 is driven by the energy stored in thebattery pack 54 that is charged by the supply of the electric power fromthe outside. Since all the driving force required for the driving themotor bicycle 67 is generated from the electric motor 65, it isnecessary to use the electric motor 65 of a high output. Also, since itis necessary for the battery pack to store all the energy required forone driving by one charging, it is necessary to use a battery packhaving a relatively large capacity. It is desirable for the ratedcapacity of the battery pack to fall within a range of 10 to 50 Ah, moredesirably 15 to 30 Ah.

Fourth Embodiment

FIGS. 13 and 14 show an example of a rechargeable vacuum cleaneraccording to a fourth embodiment. The rechargeable vacuum cleanercomprises an operating panel 75 which selects operation modes, anelectrically driven blower 74 comprising a fun motor for generatingsuction power for dust collection, and a control circuit 73. A batterypack 72 according to the second embodiment as a power source for drivingthese units are housed in a casing 70. When the battery pack is housedin such a portable device, the battery pack is desirably fixed withinterposition of a buffer material in order to prevent the battery packfrom being affected by vibration. Known technologies may be applied formaintaining the battery pack at an appropriate temperature. While abattery charger 71 that also serves as a setting table functions as thebattery charger of the battery pack according to the second embodiment,a part or all of the function of the battery charger may be housed inthe casing 70.

While the rechargeable vacuum cleaner consumes a large electric power,the rated capacity of the battery pack is desirably in the range of 2 to10 Ah, more preferably 2 to 4 Ah, in terms of portability and operationtime. The nominal voltage of the battery pack is desirably in the rangeof 40 to 80 V.

Examples of the invention will be described in detail with reference todrawings.

Example 1 Manufacture of Positive Electrode

LiCoO₂ was used as the positive electrode active material, and agraphite powder was blended as a conductive agent in a proportion of 8%by weight relative to the total weight of the positive electrode whilePVdF was blended as a binder in a proportion of 5% by weight relative tothe total weight of the positive electrode. A slurry was prepared bydispersing these materials in N-methylpyrrolidone (NMP). The slurryobtained was applied on an aluminum foil with a thickness of 15 μm andan average crystal grain size of 4 μm, followed by drying and pressingto manufacture a positive electrode with an electrode density of 3.3g/cm³.

Manufacture of Negative Electrode

Li₄Ti₅O₁₂ particles with an average particle diameter of 0.90 μm and atrue density ρ₁ of 3.23 g/cm³ were prepared as the first negativeelectrode active material particles. Li₄Ti₅O₁₂ particles with an averageparticle diameter of 3.40 μm and a true density ρ₂ of 3.28 g/cm³ werealso prepared as the second negative electrode active materialparticles. The difference in the true densities (ρ₂−ρ₁) is 0.05 g/cm³. Aslurry was prepared by mixing 85 parts by weight of the first negativeelectrode active material particles, 5 parts by weight of the secondnegative electrode active material particles and 10 parts by weight ofPVdF as a binder in N-methyl pyrrolidone. The slurry obtained wasapplied on an aluminum foil with a thickness of 15 μm and an averagecrystal grain size of 4 μm, followed by drying and pressing tomanufacture a negative electrode. The (F₁/F₂) value of this negativeelectrode was 6.91.

Preparation of Nonaqueous Electrolyte

EC, PC and GLB were mixed in a volume ratio (EC:PC:GLB) of 1:1:4, and anonaqueous electrolyte was prepared by dissolving LiBF₄ in the mixedsolvent at a concentration of 2 M.

Assembly of Battery

After impregnating a separator made of a polyethylene porous film withthe nonaqueous electrolyte, the positive electrode was covered with theseparator. A coiled electrode group was manufactured by coiling thepositive electrode, the negative electrode and the separator so that thenegative electrode faces the positive electrode with interposition ofthe separator. The electrode group was formed into a flat shape bypressing. The flat-shaped electrode group was inserted into a case madeof an aluminum-containing laminate film with a thickness of 0.1 mm, anda flat-type nonaqueous electrolyte battery with a thickness of 3.0 mm, awidth of 35 mm and a height of 62 mm as shown in FIG. 1 wasmanufactured.

The battery obtained was subjected to a cycle test in which a charginguntil the battery voltage of 2.7 V at a charge rate of 1 C at 45° C. anda discharging until the battery voltage of 1.5 V at a discharge rate of1 C are performed repeatedly. The result showed that the cycleperformance was excellent since the battery capacity reached 80% of thefirst cycle discharge capacity at 1539 cycles.

Examples 2 to 36 and Comparative Examples 1 to 6

The battery was manufactured by the same method as in Example 1, exceptthat the construction of the negative electrode or nonaqueouselectrolyte was changed as shown in Tables 1 to 5.

TABLE 1 First negative electrode active material particles Secondnegative electrode Difference Peak (Particle diameter [μm]) activematerial particles in true frequency (specific surface area [g/m²])(Particle diameter [μm]) density ratio (true density [g/cm³]) (truedensity [g/cm³]) (ρ₂ − ρ₁) (F₁/F₂) Nonaqueous electrolyte Example 1Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.05 6.91 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm)(8.1 g/m²) (3.23 g/cm³) (3.40 μm) (3.28 g/cm³) Example 2 Li₄Ti₅O₁₂Li₄Ti₅O₁₂ 0.06 6.83 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.93 μm) (7.1 g/m²)(3.22 g/cm³) (3.40 μm) (3.28 g/cm³) Example 3 Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.066.88 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.85 μm) (20.2 g/m²) (3.22 g/cm³)(3.40 μm) (3.28 g/cm³) Example 4 Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.04 6.942M-LiBF₄/EC + PC + GBL(1:1:4) (0.78 μm) (48.8 g/m²) (3.24 g/cm³) (3.40μm) (3.28 g/cm³) Example 5 Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.03 6.91 2M-LiBF₄/EC +PC + GBL(1:1:4) (0.67 μm) (99.2 g/m²) (3.25 g/cm³) (3.40 μm) (3.28g/cm³) Example 6 Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.01 6.87 2M-LiBF₄/EC + PC +GBL(1:1:4) (0.90 μm) (8.1 g/m²) (3.23 g/cm³) (3.39 μm) (3.24 g/cm³)Example 7 Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 1.00 6.90 2M-LiBF₄/EC + PC + GBL(1:1:4)(0.90 μm) (8.1 g/m²) (3.23 g/cm³) (3.55 μm) (4.23 g/cm³) Example 8Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 2.38 6.92 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm)(8.1 g/m²) (3.23 g/cm³) (3.93 μm) (5.61 g/cm³) Example 9 Li₄Ti₅O₁₂Li₄Ti₅O₁₂ 0.05 2.21 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm) (8.1 g/m²)(3.23 g/cm³) (3.40 μm) (3.28 g/cm³) Example 10 Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.055.08 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm) (8.1 g/m²) (3.23 g/cm³)(3.40 μm) (3.28 g/cm³)

TABLE 2 First negative electrode active material particles Secondnegative electrode Difference Peak (Particle diameter [μm]) activematerial particles in true frequency (specific surface area [g/m²])(Particle diameter [μm]) density ratio (true density [g/cm³]) (truedensity [g/cm³]) (ρ₂ − ρ₁) (F₁/F₂) Nonaqueous electrolyte Example 11Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.05 14.75 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm)(8.1 g/m²) (3.23 g/cm³) (3.40 μm) (3.28 g/cm³) Example 12 Li₄Ti₅O₁₂Li₄Ti₅O₁₂ 0.05 19.80 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm) (8.1 g/m²)(3.23 g/cm³) (3.40 μm) (3.28 g/cm³) Example 13 Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.036.81 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm) (8.1 g/m²) (3.23 g/cm³)(2.13 μm) (3.26 g/cm³) Example 14 Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.06 6.722M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm) (8.1 g/m²) (3.23 g/cm³) (25.62μm) (3.29 g/cm³) Example 15 Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.08 6.66 2M-LiBF₄/EC +PC + GBL(1:1:4) (0.90 μm) (8.1 g/m²) (3.23 g/cm³) (48.12 μm) (3.31g/cm³) Example 16 Li₄Ti₅O₁₂ MnO₂ 0.79 6.33 2M-LiBF₄/EC + PC + GBL(1:1:4)(0.90 μm) (8.1 g/m²) (3.23 g/cm³) (3.36 μm) (4.02 g/cm³) Example 17Li₄Ti₅O₁₂ FeS 0.32 6.45 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm) (8.1g/m²) (3.23 g/cm³) (4.23 μm) (3.55 g/cm³) Example 18 Li₄Ti₅O₁₂ FeS₂ 0.396.91 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm) (8.1 g/m²) (3.23 g/cm³)(4.83 μm) (3.62 g/cm³) Example 19 Li₄Ti₅O₁₂ CuO 1.59 7.38 2M-LiBF₄/EC +PC + GBL(1:1:4) (0.90 μm) (8.1 g/m²) (3.23 g/cm³) (5.23 μm) (4.82 g/cm³)Example 20 Li₄Ti₅O₁₂ Cu₄O(PO₄)₂ 1.79 7.21 2M-LiBF₄/EC + PC + GBL(1:1:4)(0.90 μm) (8.1 g/m²) (3.23 g/cm³) (2.13 μm) (5.02 g/cm³)

TABLE 3 First negative electrode active material particles Secondnegative electrode Difference Peak (Particle diameter [μm]) activematerial particles in true frequency (specific surface area [g/m²])(Particle diameter [μm]) density ratio (true density [g/cm³]) (truedensity [g/cm³]) (ρ₂ − ρ₁) (F₁/F₂) Nonaqueous electrolyte Example 21Li₄Ti₅O₁₂ MoO₃ 1.54 6.13 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm) (8.1g/m²) (3.23 g/cm³) (3.15 μm) (4.77 g/cm³) Example 22 Li₄Ti₅O₁₂ TiO₂ 1.536.08 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm) (8.1 g/m²) (3.23 g/cm³)(3.04 μm) (4.86 g/cm³) Example 23 Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.05 6.911.2M-LiPF₆/EC + MEC(1:2) (0.90 μm) (8.1 g/m²) (3.23 g/cm³) (3.40 μm)(3.28 g/cm³) Example 24 Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.05 6.93 2M-LiBF₄/EC + PC +GBL(1:1:4) (1 μm) (8.0 g/m²) (3.23 g/cm³) (3.40 μm) (3.28 g/cm³) Example25 Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.06 6.95 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.5 μm)(9.1 g/m²) (3.23 g/cm³) (3.40 μm) (3.28 g/cm³) Example 26 Li₄Ti₅O₁₂Li₄Ti₅O₁₂ 0.03 6.81 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm) (8.1 g/m²)(3.23 g/cm³) (2 μm) (3.26 g/cm³) Example 27 Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.086.66 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm) (8.1 g/m²) (3.23 g/cm³) (50μm) (3.31 g/cm³) Example 28 Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.03 6.81 2M-LiBF₄/EC +PC + GBL(1:1:4) (0.90 μm) (8.1 g/m²) (3.23 g/cm³) (3 μm) (3.26 g/cm³)Example 29 Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.08 6.66 2M-LiBF₄/EC + PC + GBL(1:1:4)(0.90 μm) (8.1 g/m²) (3.23 g/cm³) (40 μm) (3.31 g/cm³) Example 30Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 2.50 6.92 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm)(8.1 g/m²) (3.23 g/cm³) (3.93 μm) (5.73 g/cm³)

TABLE 4 First negative electrode active material particles Secondnegative electrode Difference Peak (Particle diameter [μm]) activematerial particles in true frequency (specific surface area [g/m²])(Particle diameter [μm]) density ratio (true density [g/cm³]) (truedensity [g/cm³]) (ρ₂ − ρ₁) (F₁/F₂) Nonaqueous electrolyte Example 31Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.02 6.94 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm)(8.1 g/m²) (3.23 g/cm³) (3.90 μm) (3.25 g/cm³) Example 32 Li₄Ti₅O₁₂Li₄Ti₅O₁₂ 2.00 6.96 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm) (8.1 g/m²)(3.23 g/cm³) (3.94 μm) (5.23 g/cm³) Example 33 Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.052.00 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm) (8.1 g/m²) (3.23 g/cm³)(3.40 μm) (3.28 g/cm³) Example 34 Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.05 20.002M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm) (8.1 g/m²) (3.23 g/cm³) (3.40μm) (3.28 g/cm³) Example 35 Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.05 1.31 2M-LiBF₄/EC +PC + GBL(1:1:4) (0.90 μm) (8.1 g/m²) (3.23 g/cm³) (3.40 μm) (3.28 g/cm³)Example 36 Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.05 21.87 2M-LiBF₄/EC + PC + GBL(1:1:4)(0.90 μm) (8.1 g/m²) (3.23 g/cm³) (3.40 μm) (3.28 g/cm³)

TABLE 5 First negative electrode active material particles Secondnegative electrode Difference Peak (Particle diameter [μm]) activematerial particles in true frequency (specific surface area [g/m²])(Particle diameter [μm]) density ratio (true density [g/cm³]) (truedensity [g/cm³]) (ρ₂ − ρ₁) (F₁/F₂) Nonaqueous electrolyte ComparativeLi₄Ti₅O₁₂ Non — — 2M-LiBF₄/EC + PC + GBL(1:1:4) Example 1 (0.90 μm) (8.1g/m²) (3.23 g/cm³) Comparative Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ −0.04 6.452M-LiBF₄/EC + PC + GBL(1:1:4) Example 2 (0.90 μm) (8.1 g/m²) (3.23g/cm³) (2.87 μm) (3.19 g/cm³) Comparative Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 2.64 6.382M-LiBF₄/EC + PC + GBL(1:1:4) Example 3 (0.90 μm) (8.1 g/m²) (3.23g/cm³) (22.12 μm) (5.87 g/cm³) Comparative Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ −0.016.66 2M-LiBF₄/EC + PC + GBL(1:1:4) Example 4 (0.90 μm) (8.1 g/m²) (3.23g/cm³) (1.51 μm) (3.22 g/cm³) Comparative Li₄Ti₅O₁₂ Li₄Ti₅O₁₂ 0.20 6.382M-LiBF₄/EC + PC + GBL(1:1:4) Example 5 (0.90 μm) (8.1 g/m²) (3.23g/cm³) (55.34 μm) (3.43 g/cm³) Comparative Li₄Ti₅O₁₂ Non — —1.2M-LiPF₆/EC + MEC(1:2) Example 6 (0.90 μm) (8.1 g/m²) (3.23 g/cm³)

Example 37 Manufacture of Positive Electrode

LiMn₂O₄ particles with an average particle diameter of 0.90 μm and atrue density ρ₁ of 5.26 g/cm³ were prepared as the first positiveelectrode active material particles. LiMn₂O₄ particles with an averageparticle diameter of 3.48 μm and a true density ρ₂ of 5.56 g/cm³ werealso prepared as the second positive electrode active materialparticles. A graphite powder as a conductive agent in a proportion of 8%by weight relative to the total weight of the positive electrode andPVdF as a binder in a proportion of 5% by weight relative to the totalweight of the positive electrode were blended to the electrode activematerial comprising 82 parts by weight of the first positive electrodeactive material particles and 5 parts by weight of the second positiveelectrode active material particles. A slurry was prepared by dispersingthese materials in N-methylpyrrolidone (NMP). The slurry obtained wasapplied on an aluminum foil with a thickness of 15 μm and an averagecrystal grain size of 4 μm, followed by drying and pressing tomanufacture a positive electrode with an electrode density of 3.3 g/cm³.

A nonaqueous electrolyte battery was manufactured by the same method asdescribed in Example 1, except that the positive electrode obtainedabove was used.

Examples 38 to 42

The battery was manufactured by the same method as in Example 37, exceptthat the construction of the positive electrode or nonaqueouselectrolyte was changed as shown in Table 6.

Comparative Example 7

The battery was manufactured by the same method as in Example 37, exceptthat the construction of the positive electrode was changed as shown inTable 6, and the negative electrode in Comparative Example 1 was used.

TABLE 6 First positive electrode active material particles Secondpositive electrode Difference Peak (Particle diameter [μm]) activematerial particles in true frequency (specific surface area [g/m²])(Particle diameter [μm]) density ratio (true density [g/cm³]) (truedensity [g/cm³]) (ρ₂ − ρ₁) (F₁/F₂) Nonaqueous electrolyte Example 37LiMn₂O₄ LiMn₂O₄ 0.30 5.83 2M-LiBF4/EC + PC + GBL(1:1:4) (0.90 μm) (4.3g/m²) (5.26 g/cm³) (3.48 μm) (5.56 g/cm³) Example 38 LiMn₂O₄ LiMn₂O₄0.25 4.32 2M-LiBF₄/EC + PC + GBL(1:1:4) (1 μm) (4.2 g/m²) (5.31 g/cm³)(3.48 μm) (5.56 g/cm³) Example 39 LiMn₂O₄ LiMn₂O₄ 0.39 6.132M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm) (4.3 g/m²) (5.26 g/cm³) (2 μm)(5.67 g/cm³) Example 40 LiMn₂O₄ LiMn₂O₄ 0.28 6.08 2M-LiBF₄/EC + PC +GBL(1:1:4) (0.90 μm) (4.3 g/m²) (5.26 g/cm³) (50 μm) (5.54 g/cm³)Example 41 LiMn₂O₄ LiMn₂O₄ 0.01 5.77 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.90μm) (4.3 g/m²) (5.26 g/cm³) (3.28 μm) (5.27 g/cm³) Example 42 LiMn₂O₄LiMn₂O₄ 2.5 5.71 2M-LiBF₄/EC + PC + GBL(1:1:4) (0.90 μm) (4.3 g/m²)(5.26 g/cm³) (4.26 μm) (7.76 g/cm³) Comparative LiMn₂O₄ Non — —2M-LiBF₄/EC + PC + GBL(1:1:4) Example 7 (0.90 μm) (4.3 g/m²) (5.26g/cm³)

The batteries manufactured in the examples and comparative examples weresubjected to a cycle test in which a charging until a battery voltage of2.7 V at a charge rate of 1 C at 45° C. and a discharging until abattery voltage of 1.5 V at a discharge rate of 1 C are performedrepeatedly. The number of cycles when the battery capacity reached 80%of the first cycle discharge capacity after repeating the cycle test isshown in Tables 7 and 8 below.

TABLE 7 Cycle life Example 1 1539 Example 2 1474 Example 3 1331 Example4 1258 Example 5 1093 Example 6 1312 Example 7 1038 Example 8 1174Example 9 1193 Example 10 1460 Example 11 1472 Example 12 1298 Example13 1338 Example 14 1348 Example 15 1299 Example 16 1378 Example 17 1383Example 18 1405 Example 19 1343 Example 20 1356 Example 21 1364 Example22 1415 Example 23 1041 Example 24 1496 Example 25 1075 Example 26 1316Example 27 1265 Example 28 1520 Example 29 1343 Example 30 1018 Example31 1316 Example 32 1487 Example 33 1267 Example 34 1282 Example 35 1192Example 36 1188 Comparative Example 1 1007 Comparative Example 2 973Comparative Example 3 981 Comparative Example 4 1006 Comparative Example5 993 Comparative Example 6 993

TABLE 8 Cycle life Example 37 1034 Example 38 1023 Example 39 1015Example 40 958 Example 41 965 Example 42 962 Comparative Example 7 863

Table 7 shows that the batteries in Examples 1 to 36 are superior to thebatteries in Comparative Examples 1 to 6 with respect to the cycleperformance. This shows that the cycle performance was improved by usingthe first active material particles with an average particle diameter of1 μm or less and a lithium diffusion coefficient of 1×10⁻⁹ cm²/sec orless at 20° C. and the second active material particles with an averageparticle diameter of 2 to 50 μm, and by increasing the true density ofthe second active material particles by 0.01 to 2.5 g/cm³ compared tothe true density of the first active material particles.

Comparisons among Examples 1 and 16 to 22 show that the cycleperformance in Example 1 using Li_(4+x)Ti₅O₁₂ (0≦x≦3) for both the firstand second active materials is superior to the cycle performance inExamples 16 to 22 in which the second active material is MnO₂, FeS,FeS₂, CuO, Cu₄O(PO₄)₂, MoO₃ or TiO₂. This shows that usingLi_(4+x)Ti₅O₁₂ (0≦x≦3) for both the first and second active materials iseffective for improving the cycle performance.

Comparisons among Examples 1, 9 to 12 and 33 to 36 show that the cycleperformance in Examples 1, 9 to 12, 33 and 34, in which the frequencyratio (F₁/F₂) of the first and second peaks in the particle diameterdistribution measured by the laser diffraction is 2 to 20, is superiorto the cycle performance in Examples 35 and 36 in which the frequencyratio (F₁/F₂) is less than 2 or exceeds 20. The cycle performance inExamples 1, 10 and 11 in which the frequency ratio (F₁/F₂) is 5 to 15 isparticularly excellent. Accordingly, the frequency ratio (F₁/F₂) isdesirably in the range of 2 to 20, more preferably 5 to 15, forimproving the cycle performance.

The cycle performance in Example 1 in which a nonaqueous electrolytecontaining EC, PC and GBL is superior to the cycle performance inExample 23 in which EC and MEC are used, and it was shown that using thethree components of EC, PC and GBL permits excellent cycle performanceto be readily obtained. As shown in Comparative Examples 1 and 6, theeffect for improving the cycle performance by using the three componentsof EC, PC and GBL is not sufficiently exhibited when only the particlesof the first negative electrode active material are used as the negativeelectrode active material, and the effect for improving the cycleperformance is evidently manifested when the particles of the first andsecond active materials are used together.

Comparison among Examples 8 and 30 to 32 show that the cycle performancein Examples 31 and 32 in which the true density difference is 0.02 to 2g/cm³ is superior to the cycle performance in Examples 8 and 30 in whichthe true density difference exceeds 2 g/cm³.

Comparison among Examples 13, 15 and 26 to 29 show that the cycleperformance in Examples 28 and 29 in which the average particle diameterof the second active material particles is 3 to 40 μm is superior to thecycle performance in Examples 13, 15, 26 and 27 in which the averageparticle diameter is out of this range.

The results in Table 8 show that cycle performance is also improved byusing the first and second active materials for the positive electrode.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A nonaqueous electrolyte battery comprising: apositive electrode; a negative electrode; and a nonaqueous electrolyte,wherein at least one of the positive electrode and the negativeelectrode comprises: a current collector made of aluminum or an aluminumalloy; and an active material layer which is laminated on the currentcollector, the active material layer containing first active materialparticles having an average particle diameter of 1 μm or less and alithium diffusion coefficient of 1×10⁻⁹ cm²/sec or less at 20° C. andsecond active material particles having an average particle diameter of2 to 50 μm, a true density of the second active material particles islarger by 0.01 to 2.5 g/cm³ than a true density of the first activematerial particles.
 2. The nonaqueous electrolyte battery according toclaim 1, wherein each of the positive electrode and the negativeelectrode comprises the current collector and the active material layer.3. The nonaqueous electrolyte battery according to claim 1, wherein adifference between the true density of the first active materialparticles and the true density of the second active material particlesis in the range of 0.02 to 2 g/cm³.
 4. The nonaqueous electrolytebattery according to claim 1, wherein a particle diameter distributionmeasured by a laser diffraction for a mixture containing the firstactive material particles and the second active material particles has afirst peak at a smaller particle diameter and a second peak at a largerparticle diameter, and the first peak and second peak satisfy thefollowing equation (1):2≦(F ₁ /F ₂)≦20  (1) where F₁ is a frequency of the first peak and F₂ isa frequency of the second peak.
 5. A nonaqueous electrolyte batterycomprising: a positive electrode comprising a current collector made ofaluminum or an aluminum alloy and an active material layer laminated onthe current collector, the active material layer containing first activematerial particles that have an average particle diameter of 1 μm orless and are represented by Li_(y)Mn₂O₄ (0≦y≦1) and second activematerial particles having an average particle diameter of 2 to 50 μm,and a true density of the second active material particles being largerby 0.01 to 2.5 g/cm³ than a true density of the first active materialparticles; a negative electrode; and a nonaqueous electrolyte.
 6. Thenonaqueous electrolyte battery according to claim 5, wherein the secondactive material particles are represented by Li_(y)Mn₂O₄ (0≦y≦1).
 7. Abattery pack comprising a nonaqueous electrolyte battery comprising apositive electrode, a negative electrode and a nonaqueous electrolyte,wherein at least one of the positive electrode and the negativeelectrode comprises: a current collector made of aluminum or an aluminumalloy; and an active material layer which is laminated on the currentcollector, the active material layer containing first active materialparticles having an average particle diameter of 1 μm or less and alithium diffusion coefficient of 1×10⁻⁹ cm²/sec or less at 20° C., andsecond active material particles having an average particle diameter of2 to 50 μm, a true density of the second active material particles islarger by 0.01 to 2.5 g/cm³ than a true density of the first activematerial particles.
 8. The battery pack according to claim 7, whereineach of the positive electrode and the negative electrode comprises thecurrent collector and the active material layer.
 9. The battery packaccording to claim 7, wherein a difference between the true density ofthe first active material particles and the true density of the secondactive material particles is in the range of 0.02 to 2 g/cm³.
 10. Thebattery pack according to claim 7, wherein a particle diameterdistribution measured by a laser diffraction for a mixture containingthe first active material particles and the second active materialparticles has a first peak at a smaller particle diameter and a secondpeak at a larger particle diameter, and the first peak and second peaksatisfy the following equation (1):2≦(F ₁ /F ₂)≦20  (1) where F₁ is a frequency of the first peak and F₂ isa frequency of the second peak.
 11. A battery pack comprising anonaqueous electrolyte battery comprising a positive electrode, anegative electrode and a nonaqueous electrolyte, wherein the positiveelectrode comprises a current collector made of aluminum or an aluminumalloy and an active material layer laminated on the current collector,the active material layer containing first active material particlesthat have an average particle diameter of 1 μm or less and arerepresented by Li_(y)Mn₂O₄ (0≦y≦1) and second active material particleshaving an average particle diameter of 2 to 50 μm, and a true density ofthe second active material particles is larger by 0.01 to 2.5 g/cm³ thana true density of the first active material particles.
 12. The batterypack according to claim 11, wherein the second active material particlesare represented by Li_(y)Mn₂O₄ (0≦y≦1).
 13. A rechargeable vacuumcleaner comprising the battery pack according to claim
 7. 14. Arechargeable vacuum cleaner comprising the battery pack according toclaim 11.